The vagus nerve is the key component of the parasympathetic branch of a human being's autonomic nervous system. The autonomic nervous system regulates many body organs that operate on a largely subconscious level, such as the heart, lungs, eyes, glands, and digestive tract. When the vagal nerve is electrically stimulated (“vagal nerve stimulation”) the operation of the autonomic nervous system is affected. Vagal nerve stimulation is FDA approved for treatment of epilepsy and for depression.
When used to treat epilepsy and depression, vagal nerve stimulation is carried out using an “open loop” protocol; a predetermined degree of stimulation is applied for a predetermined period of time, without regard for the affect that the stimulation is actually having on the patient. As a result, patients can be over-stimulated, causing side effects (examples include, but are not limited to hoarseness of breath, sleep apnea, etc.) that some patients consider to be intolerable. These side effects also preclude use of this technology with other conditions that may otherwise benefit from its use as a first line treatment (e.g., chronic pain, sleep disorders).
It has also been proposed to use a “closed-loop” vagal nerve stimulation protocol to treat cardiovascular issues. For example, patent application publication US 2006/0122676 A1 discloses a device in which vagal nerve stimulation is used to protect the myocardium from further remodeling and predisposition to fatal arrhythmias after the patient has had a heart attack. Some embodiments of the device regulate the vagal nerve stimulation in accordance with the patient's response thereto, such response being determined by measuring the patient's ECG, blood pressure, heart rate, “and the like”, and some embodiments allow the patient to initiate the vagal nerve stimulation.
Certain non-cardiovascular diseases, such as anxiety, depression, post-traumatic stress disorder, inflammatory disorders, sleep disorders and chronic pain involve the autonomic nervous system. And, further, behavior of the autonomic nervous system can reflect the behavior of core brain systems involved in these disorders. In other words, autonomic nervous system attributes can be used as an indicator of brain behavior such that more complicated and dangerous solutions (e.g., direct cortical monitoring) are unnecessary to close the loop. It would be advantageous to be able to treat such non-cardiovascular diseases using a closed-loop vagal nerve stimulation protocol to avoid applying excessive stimulation and thereby avoid the side effects that such excessive stimulation can create whilst maximizing the effectiveness/timing of said stimulation with regards to individualized patient profiles/responses.